224MB sounds ‘odd’…I’d expect multiples of 128 so 256/512/1024 (i.e. 1 Ggb).
With 512mb or a 1GB RAM and assuming XP then it ‘could’ be okay (assuming running XP…or Linux!). I was in a similar situation..upgraded a hard-drive, reinstalled all software, added memory, added wireless (a PCMCIA wireless card, if you have the slot for it, is a much neater solution than a dongle).
TBH doing all this put me on for another year but eventually I bought a new one…benefits are it’s lighter, longer battery life, blu-tooth (love to use my blu-tooth mouse), USB2, bigger hard-drive…).
I’d say that if you can still get an XP laptop then perhaps get one…otherwise you want a reasonably well specced machine to run Vista….if you can wait we ‘should’ be seeing Windows 7 in the next year (think Rumour is by the end of the year)…there is never a ‘right’ time…